This invention relates to dual-in-line (DIL) connector assemblies for mounting integrated circuit (IC) components and the like to circuit boards such as printed circuit boards, and, more particularly, to connectors of this type having a so-called closed-entry, closed-bottom integral structure.
Areas of consideration to be addressed in the design of a DIL connector are its proper attachment to the circuit board and the ability to removably mount an lC without damage or undue force. Present practices of securing a DIL connector to a circuit board by its pins include both soldering techniques and mechanical techniques. The word "pin" as used herein represents that portion of the contact which protrudes from the bottom surface of the connector assembly.
Known mechanical techniques include the use of pin configurations designed to provide an interference fit in the associated metallized holes of the circuit board. Known interference-fit type pin designs have the problem of circuit board hole tolerance requirements.
Securing DIL connectors to the circuit boards by soldering may be accomplished through several processes. So-called wave soldering is an example of an efficient mass production technique. As part of this technique, flux material is first used to clean the contacts and to promote the joining of the metals in the soldering process. With the contacts so prepared, and protruding through the associated holes in the circuit board, the underside of the board is subjected to a "wave" of solder. Following a suitable cooling period, the flux is rinsed from the assembly, usually by applying a hot water spray. The flux cleaning step is included since flux remaining in the connector tends to corrode the contacts in the socket area over a period of time. It is, thus, essential to remove as much of the flux from the connector assembly as possible. As used herein, the phrase "socket area" refers to the chamber portion of the connector that houses the part of the contact which is intended to engage the IC lead.
Known soldering techniques, in spite of their efficiencies, give rise to substantial problems relating to the deposited solder itself as well as the flux material. For example, solder "bridging" may occur. This is the condition wherein the solder bridges over from the connector pin and its associated circuit board hole to an adjacent circuit making electrical contact therebetween.
Bridging tends to occur more frequently in cases where portions of the contact remain above the circuit board in close proximity to other circuit paths. When these portions of the contacts are parallel to the plane of the board, bridging is more likely to occur.
"Solder wicking" is another problem which is associated with the soldering of these contacts. This is a condition in which molten solder travels along the pin portion of the contact up into the connector assembly, and in particular, into the socket area. Wicking is particularly undesirable in connector structures having contacts configured to provide a form of spring-loaded interference fit with the IC lead since the solder clinging to the contact may hamper its bending ability. Altered flexibility of the contact spring may adversely affect the characteristics of the electrical connection between the contact and an IC lead.
The problem of wicking may be compounded in cases where soldering is performed with the IC already mounted into the connector assembly. Under this condition, the solder may bridge over onto the IC lead as well. This, of course, makes removal of the IC difficult at best and will likely lead to permanent damage to either or both the contact and the IC, especially if removal of the latter is attempted.
With present soldering techniques, the design and configuration of the connector assembly itself must be relied upon to minimize or eliminate the aforementioned problems. Known solutions for minimizing or eliminating occurrences of solder bridging have mainly involved the use of simple straight pins. Wicking has generally been countered by providing the connector assembly with some form of a so-called closed-bottom structure. A combination of the two is, of course, also possible.
A closed-bottom structure is one in which the openings in the bottom surface of the connector assembly, through which the pins emerge, are narrowly restricted in size so as to be little more than the cross-section of the pins themselves. This may be accomplished either by having the connector assembly holes physically limited in size, or by using an external underlay of suitably non-conductive material such as polyester strips. The underlay is intended to effectively close or narrow what otherwise would be considered an open-bottom structure. The use of self-adhesive sheet materials for this application is also known.
A connector designed with a closed-bottom, per se, structure requires that its contacts be inserted from the top in unitary connector constructions. In such a case, a closed-entry structure is not possible; it would have to be achieved by some external means, such as an open-bottom which is subsequently covered by an underlay.
When using an underlay to create an effective closed-bottom configuration, one cannot ignore that proper assembly and positioning of the underlay is absolutely essential, and, thus, tolerances tend to become critical.
With either of the closed-bottom solutions discussed above, if flux contamination does occur in the socket area (a distinct possibility in mass production techniques), it is extremely difficult to effect satisfactory rinsing of the flux from this area. This problem is, of course, alleviated by an open-bottom structure, but, as already indicated, such designs fall prey to the hereinbefore discussed problems of solder bridging and wicking.
While the use of substantially straight pins does represent a relatively satisfactory solution for avoiding solder bridging, various practical and commercial reasons have made it advantageous to utilize a contact configuration which is appreciably bent over the course of its length below the socket area of the connector assembly (and specifically the pin portion). This is particularly the case where the DIL contact has been designed as a singular element structure to achieve a spring-loaded interference contact with the IC lead, having the free end of the contact in the socket area extending at an angle to the direction of insertion of the IC lead. This configuration is desirable in that it enables good electrical contact with and securely holds the IC lead. It also allows an acceptably low IC insertion force and a substantially damage free removal thereof. However, it does necessarily complicate installation into the connector housing, especially if a closed-entry, closed-bottom structure is contemplated.
This invention, therefore, provides a closed-entry and closed-bottom connector assembly which avoids wicking and bridging and facilitates flux removal. The closed-entry, closed-bottom aspects are achieved within the structure of the connector itself as opposed to any external measures such as an underlay. The assembly utilizes a singular-element contact configuration shaped to achieve the aforementioned highly desirable spring-loaded type interference fit with the IC lead. The structure effectively eliminates solder wicking and bridging while facilitating flux rinsing to avoid corrosion.
With more specific regard to the aspects of nounting the IC to the connector, a commercially acceptable connector should provide: (1) guidance of the IC lead into proper (non-destructive) engagement with the connector contact in the socket area; (2) secure, but removable, contact engagement with the IC lead without requirement for undue insertion or removal forces; and, (3) continuous, reliable electrical contact between the IC lead and the contact. The contact configuration of a connector assembly providing these attributes should nevertheless be simple enough to minimize fabrication and installation costs and problems.
The desire to have a closed-entry structure, alluded to hereinbefore, stems from the need to guide the IC lead into proper, smooth engagement with the connector contact in the socket area. It also prevents insertion of deformed or oversized contacts or probes avoiding a jarring collision which could cause permanent deformation or breakage of the contact. A closed-entry structure, similar to a closed-bottom structure, is one where the opening of the connector into the socket area for insertion of the IC lead is restricted in size so as to be not substantially greater than the cross-sectional dimensions of the IC lead itself. Of course, the opening into the socket area can be beveled to facilitate guidance of the IC lead.
An alternative to closed-entry construction of the connector housing is to provide relatively more complex contact structures in the socket area wherein the contact itself guides the IC lead and facilitates non-destructive insertion and withdrawal. Such complex contacts would necessarily cost more to manufacture. Special fabrication and assembly considerations are likely to be required for such contacts, as are larger dimensions and more material.
The need to provide proper guidance of the IC lead during insertion is especially essential in those known cases where the connector contact is singular. Deformation of such a contact would impair its ability to achieve good electrical contact with the IC and to effectively hold it in place. Use of this contact configuration normally would be precluded in a unitary closed-entry, closed-bottom connector assembly.
Nevertheless, the singular contact configuration is preferred for various reasons, including economy. The importance of contact configuration cannot be underestimated in attaining the goal of a reliable, cost competitive, mass produceable connector assembly. The IC should be securely held in the socket area by the connector contact and yet allow removal of the former without undue withdrawal forces being required or damage occurring.
This invention, therefore, provides a DIL connector assembly of the closed-entry, closed-bottom type in which the contacts are fabricated from relatively inexpensive material, proper guidance of the IC leads into the socket areas is assured and gas-tight contacts are effectively achieved. The invention, however, enables relatively low and non-destructive insertion and withdrawal force requirements.